1. Field of the Invention
This invention pertains to the field of automatic transmission control and to hydraulic actuation of a brake that holds a component of a gearset against rotation.
2. Description of the Prior Art
A servo mechanism used to operate a brake band in an automatic transmission conventionally includes a hydraulically actuated piston, a piston chamber, within which a piston moves in response to the presence and absence of hydraulic pressure in the chamber.
U.S. Pat. No. 4,881,453 describes a servo mechanism in a housing, whose interior contains circumferentially spaced locating pilot means that cooperate with a socket cavity to orient the housing. The interior of the housing contains a piston chamber within which a piston is slidably received. An actuating pin is secured to the piston, and the actuating pin is slidably received within a pilot bore that extends longitudinally outward from the piston chamber inward of a pin pilot presented from the housing of the servo mechanism to guide the actuating pin as it operates within the interior cavity of the transmission casing. The actuating pin is also secured to a friction band assembly associated with the planetary gearset.
A cover is secured to the transmission casing to act with the closure face, thereby sealing the socket cavity and interior of the case from atmosphere. The cover also acts with the housing to close one end of the piston chamber, thereby defining a pressure chamber to which the head of the piston is exposed.